Hot oils or fats are often used not only once, but are utilized in deep fryers over a longer period for successively preparing different foods. The oil or fat is decomposed by oxidation at the hot operating temperatures between approximately 120° C. and 180° C. and undesirable chemical products such as free fatty acids and polymers are formed, which not only impair the taste, but may also have adverse health effects.
In order to avoid replacing frying oils or fats too early or too late, measuring devices are used for measuring the state of oils or fats, including tests for their electrical properties. Measuring the dielectric constant, which is a reliable measure of the degree of decomposition of fats or oils, is particularly suitable.
EP 1 046 908 A2, for example, describes a measuring device for measuring the state of an oil or fat, which has a housing which contains the electronic analyzer units and a data display, as well as a tubular connecting element with a sensor situated at its tip which may be directly immersed into the hot oil or fat and is suitable for determining the dielectric constant. The sensor and the electronic analyzer circuit are electrically connected via a cable laid freely within the connecting element.
DE 101 63 760 A1 describes a refinement of the above-mentioned measuring device. In the measuring device presented therein, the electrical conductors between the sensor and the electronic analyzer circuit are formed by metallic conductors printed on a ceramic substrate. The tubular connecting element is shaped in such a way that it surrounds most of the substrate and narrows downward in such a way that only the area of the substrate on which the sensor is situated is accessible from the outside. An insulating sealing adhesive is introduced and cured between the substrate and the connecting element, so that there is no electrical connection between the connecting element and the electrical conductors. In addition, a temperature-stable seal is achieved, which prevents the oil from penetrating inside the connecting element. A temperature sensor may also be provided, whose measurement results may also be processed by the electronic analyzer circuit.
The disadvantage of this measuring device is that the measured values are often greater than the actual values despite the use of reliable sensors and suitable electronic analyzer circuits.
Accordingly, it is desirable to provide a measuring device that would deliver more accurate and more reliable measurement results.